Make really slow frames clearer in the performance page bar chart

Currently a slightly slow frame (32ms) which a user is unlikely to notice unless it is a glitch in the middle of a smooth animation looks the same as catastrophic jank (200+ms)

Idea: rather than showing a bar chart, show a timeline (perhaps with gaps omitted for periods of inactivity). That way, jank for 300ms would look visually longer than jank for 32 ms.
This is similar to what Chrome DevTools does where they show the frame rate per ms in the performance page instead of a bar chart.
A bonus of this design is it makes it easier to link up time ranges in the flame chart with the bar chart as both now have a consistent X axis. This makes it practical to visualize what time range from the flame chart is visible.

Risk of this approach: makes it less clear how long each frame took to render.
https://user-images.githubusercontent.com/1226812/121062165-9c2b8480-c779-11eb-9081-0a861a942ae2.mp4

パフォーマンスページの現在のフレーム棒グラフから始め、issueで説明されているChrome DevToolsのパフォーマンスビューとその挙動を比較します。32 msのフレームと200+ msのフレームを視覚的に区別でき、時間範囲をflame chartに合わせられ、かつ各フレームのレンダリング時間も伝えられるタイムラインを定義します。

索引モデルが issue の本文から書いたものです。